Recently, as an endoscope apparatus for observing the inside of a body cavity of a living body, electronic endoscope apparatuses which obtain an image of a living body based on reflected light reflected from a living body which is irradiated by an illuminating light, and display the image on a monitor, or the like, have come into wide use in various field. Also, many endoscope apparatuses include a forceps port, and via a probe introduced into the body cavity through this forceps port, the biopsy and treatment of tissues in the body cavity can be performed.
As the above-described endoscope apparatus, an ultrasonic tomographic imaging apparatus that uses an ultrasonic wave and the like are also known. Further, as an example, an optical tomographic imaging apparatus that employs light interference of low coherence light may also be used. In those optical tomographic imaging apparatuses, a low coherence light emitted from a light source is split into a measuring light and a reference light. Thereafter, reflected light, which is the measuring light reflected by a measured object when the measuring light is irradiated onto the measured object, is guided to a light multiplexing means. Meanwhile, the reference light is guided to the light combining after the optical path length thereof is changed. Then, the reflected light is combined with the reference light via the light combining means, and the interference light produced by the mixing of the reflected light with the reference light is measured via heterodyne detection or the like.
Further, when the measuring light is irradiated onto the measured object, a probe is used, the probe which is inserted into the body cavity from a forceps through a forceps channel. The probe includes an optical fiber for guiding the measuring light and a rotatable mirror which is provided at the tip of the optical fiber for reflecting the measuring light in the orthogonal direction. The measuring light is irradiated on the measured object in the body cavity from the probe, and the reflected light reflected from the measured object is guided to the light combining means again through the optical fiber of the probe. Here, by utilizing the fact that interference light is detected when the optical path lengths of the measuring light and the reflected light equate to the optical path length of the reference light, the measuring position (the depth of measurement) in the measured object is changed, by changing the optical path length of the reference light. This is a so-called OCT measurement (refer to Patent Document 1).